In recent years, with the all-round upgrading of industrial products, especially automatic industrial products, there is an increasing demand for the performance of a lubricant. Newly enacted environment protection laws and regulations have put forward strict restrictions on the using amount of a lubricating oil additive containing sulfur, phosphor, or chorine. At present, conventional anti-wear agents for lubricating oils include sulfur-based anti-wear agents (e.g., sulfurized alkenes, vulcanized esters, and vulcanized oils), phosphorous-based anti-wear agents (e.g., phosphates, phosphites, and alkyl phosphonates), halogen-based anti-wear agents (chlorinated paraffins, chlorohydrocarbons, and chlorinated fatty acids), organic metal anti-wear agents (lead naphthenates and dialkyldithiophosphates (ZnDDP)), etc.
With the rapid development of modern industry, and the constant improvement of people's health consciousness and their demands for the environment, it will be increasingly difficult for theses conventional anti-wear agents to satisfy harsh operating conditions and the requirements generated in the development of times. For instance, use of chlorine-based anti-wear agents, due to the toxicity thereof, has already been prohibited in some regions, such as the U.S. and Western Europe. Lead naphthenate is also being eliminated gradually due to issues of ecology and toxicity. Use of sulfur- and phosphorous-based anti-wear agents and ZnDDP, have already been internationally limited because the phosphorous or sulfur contained therein would poison a three-way catalyst in an exhaust gas converter, affect measurement accuracy of an oxygen sensor, and produce toxicity to the ecological environment.
It is exactly these enormous challenges confronted by conventional anti-wear agents for lubricating oils that have brought forth a research hotspot into nanomaterials as anti-wear agents for lubricating oils. Nanomaterials are new materials developed since the mid-1980s, and have extraordinary features different from those of any microcosmic atoms, molecules, or any macroscopic substances. New lubricating materials prepared based on nanomaterials, as lubricating oil additives, achieve anti-friction and anti-wear functions based on the characteristics of the nanoparticles per se, and contribute to tribology performance in a different manner from conventional lubricating oil additives which take advantages of structural features thereof to achieve anti-friction and anti-wear functions. Due to small granularity of nanoparticles, they get to a friction surface more easily, which facilitates formation of a thicker surface film. The surfaces of a friction pair can thus be better separated, thereby improving anti-friction and anti-wear effects.
A dendrimer is a highly branched three-dimensional molecule having a rather regular and controllable structure, and a large number of functional end groups. The concept of synthesizing dendrimers through gradual repetition was first reported by Vogtle et al. in 1978, followed by actual synthesis of dendrimers by the Tomalia group. Since then, dendrimers have become scientists' focus of attention. The molecule per se is nano-scaled, and the molecular weight distribution thereof can reach monodispersity, and meanwhile, a dendrimer has amino functional groups that increase geometrically and can be readily modified on a surface thereof. These structural features render it possible to effectively disperse the dendrimer in a lubricating oil, thus satisfying basic requirements of a nano additive for lubricating oils. However, a dendrimer used as an anti-wear additive for lubricating oils has not yet been reported so far.